Pure chlorine is dangerous to handle and rarely used to chlorinate residential swimming pools. Commonly, chlorine has been introduced into swimming pool water by adding chemicals which decompose to yield chlorine. This technique, however, requires considerable labor to repetitively test the pool water and add the required chemicals.
It is becoming increasingly popular to equip swimming pool systems with devices which generate chlorine slowly at a rate comparable to that required by the pool and to generate the chlorine from chemicals which are relatively safe to handle. U.S. Pat. Nos. 3,563,879, granted Feb. 16, 1971, to J. M. Richards et al. for "Electrolytic Chlorine Generator" and 4,439,295, granted Mar. 27, 1984, to J. M. Richards for "Chlorine Generating Apparatus" disclose one breed of such devices.
The Richards' generators subject a sodium chloride solution to electrolysis to generate chlorine and hydrogen gases under pressure. The resulting gases are injected into the pool water return line. Both of the Richards' generators employ a fairly complex membrane-type electrolytic structure in an attempt to separate the chlorine and hydrogen gases, mixtures of which are highly explosive. Furthermore, the electrolytic decomposition of a salt solution in the Richards' generators also produces a sodium hydroxide solution byproduct which is introduced into the pool water and which can complicate the problem of maintaining a desired pH balance in the pool.
It is also well known that chlorine gas can be generated by electrolyzing an aqueous solution containing hydrochloric acid. A swimming pool chlorinating system of this type is disclosed in U.S. Pat. No. 3,351,542, granted Nov. 7, 1967, to C. F. Oldershaw et al. for "Electrolytic Chlorination and pH Control of Swimming Pool Water". Oldershaw et al. draw a solution of hydrochloric acid through an electrolytic cell where the solution is converted to a froth of chlorine, hydrogen and mild hydrochloric acid. This froth is sucked into the pool water circulating pump intake for mixing with the pool water.
The Oldershaw et al. system directs the corrosive chlorine, hydrogen, hydrochloric acid froth into the pool pump, and this is not desirable. Also, the repeated introduction of even mild hydrochloric acid may upset the pool pH balance. Oldershaw, et al. rely on a fairly complex combination of a capillary tube and a timer-controlled valve to regulate the flow of hydrochloric acid solution into the system. Also, there appears to be no special precautions in the Oldershaw et al. system for handling a potentially explosive mixture of chlorine and hydrogen.
There continues to be a need for a simple and safe chlorine generating system for use with residential swimming pools.